Ask Mr. Smarty Plants

Ordinarily, the timing of transplanting is dependent on the climate in which the plant is being grown. The worst danger to a plant being moved is transplant shock. If, as its roots are struggling to get nutrients out of the soil and pass that and water up to the leaves that are struggling to manufacture food for the plant, the plant has to face extreme heat or extreme cold, it will probably not survive. In a climate as warm as yours, the best transplant time would probably be around November. You are not likely to have a severe freeze that can kill the exposed plants that early in the year, and most of those plants will have gone into a state of semi-dormancy anyway.

The most difficult plants are the woody ones-trees and shrubs. Just be careful and don't get in over your head. If you have to damage a too-large tree or shrub to get it moved, it probably won't do well and neither will you. From About.com: Landscaping we found this website on Transplant - Transplanting Trees and Shrubs.  If there are specific plants you want to transplant, you can Google "transplant iris" (for example) and you will no doubt find several good websites with information on that specific plant or type of plant. Another good website just on transplanting in general is this Michigan State University Extension article Transplanting. 

And, finally, spend the time between now and the actual transplanting preparing both your garden and the plants that are going to move to your garden. You will note some of the information on transplanting woody plants advises trimming roots some time before the actual move. You probably will also want to trim the tops of the plants to make up for the loss of roots in the move. And certainly you should prepare the soil in your garden, mixing in compost and making sure the drainage is good. Then, when it cools off and you're ready to start moving plants, everything will be ready. Hopefully, you will be, too.